1. Field of the Invention
The invention relates to a process for producing metallic components which comprise an opening and/or a hollow space by selective laser sintering and/or laser melting, where single-component or multicomponent metallic powder is melted in layers at appropriate cross-sectional regions by using laser radiation. The process according to, the invention relates in particular to a selective laser melting (SLM) process.
2. Description of the Related Art
An example of the selective laser melting (SLM) process is described in laid-open specification DE 195 11 772 A1, in which an apparatus solidifies powder material to produce a three-dimensional object by successively solidifying layers of a pulverulent structural material at respective cross-sectional regions of the object, for example, by electromagnetic radiation or particle radiation. According to this document, the powder material is applied in powder layers to a support, which is preferably equipped with a substrate plate (substrate). After a powder layer has been applied to the substrate plate, a scanner mirror is used to deflect a laser beam onto specific layer regions in a targeted manner, such that the metal powder located there is melted and then solidifies. After a first layer has been formed, the support is lowered downwards in the installation space by a layer thickness, and a new powder layer is built up over the preceding layer by the coater. After this powder layer has been applied, a laser beam is again directed at appropriate sites of the powder material in a targeted manner to selectively melt individual powder regions.
These process steps are performed repeatedly such as to produce a finished component which, after it has been freed of the remaining, unsolidified powder, substantially forms the finished component.
European patent application EP 1 358 855 A1 likewise describes a process for producing products by freeform laser sintering using an SLM process, wherein a plurality of metallic or non-metallic products are constructed on a substrate plate. According to this document, retaining webs (also referred to as supports in the document), which connect the product to be constructed to the substrate plate, are used to prevent the individual objects from lying in a powder bed in undefined form and to protect against displacement during the construction process. The retaining webs also make it easier for the individual objects to be detached from the substrate plate. The retaining webs are produced by the SLM process. So that the products can be detached more easily from the substrate plate, the retaining webs are provided with predetermined breaking points, where there is a reduction in the strength of the support along the outer contour of the products. Once the construction process has been completed, the non-solidified powder is removed from the installation space, the substrate plate together with the products located on it is taken from the system and the individual products are detached from the substrate plate by subjecting the predetermined breaking points to bending stresses. In this case, the predetermined breaking points serve exclusively for the one-off detachment of the products from the substrate plate or the process-related retaining webs.
The process of fracture splitting, together with the subsequent piecing together of the components, has emerged particularly in the field of application of automotive engineering, see, e.g., DE 100 22 884 A1. In this case, by way of example, connecting rods for internal combustion engines are produced from a ductile starting material by forging, where the still glowing forged blank is cooled locally by water jets and thereby embrittled. After the embrittlement, the connecting rod head can be separated. The rest of the connecting rod remains in the original, ductile microstructure. After this treatment, the connecting rod head, after it has been cooled, is split by fracture splitting. Bearing elements and a shaft element are inserted therein and the split connecting rod is then pieced together again.
Laid-open specification DE 10 2007 059 865 A1 likewise describes an SLM process and in paragraphs 3 and 4 explicitly sets forth the difference between selective laser melting and laser sintering processes.
The prior art for SLM processes is based on the concept of obtaining the parts produced by an SLM process as directly as possible from the process, of providing as far as possible no remachining processes therefor and of generating as far as possible single-piece components from the SLM process.
Furthermore, to produce components having closed hollow spaces it is necessary in the prior art for SLM processes to provide outlet holes through which the unsolidified powder material trapped in the hollow spaces can trickle out, in which case these outlet holes are to be closed by a plug once the hollow spaces have been emptied. In addition, in the prior art for SLM processes it is only possible to a limited extent to provide openings in an SLM component with a coating, with thermal aftertreatment and/or with a component to be arranged contiguously.
The prior art for fracture splitting processes, which provides for subsequent piecing together of the parts, is limited exclusively to castings, forgings and/or parts produced by cutting.